The format 6 for ABINIT pseudopotentials allows to use pseudopotentials
generated from the FHI98PP code (Fritz-Haber-Institute, Berlin).
This code is available at this URL.

A few lines must be added to the file generated by the FHI98PP code,
and are described in the present file. ABINITv1.9 is able to
read format 6 pseudopotential files without core correction.
ABINITv2.2 is able to read them with core correction (thanks to AF).

We will suppose that the user has been able to generate a cpi file from the FHI98PP code.
There is one such file in the ~abinit/tests/Psps_for_tests directory,
with the name al_h.cpi (the FHI98PP code generated a file named al:h.cpi,
but the name was changed, to allow portability under DOS/Windows) .
It begins by:

For the purpose of generating the corresponding file readable by ABINIT (also
found in the ~abinit/tests/Psps_for_tests directory, with the name 13al.981214.fhi),
the following seven lines have been added at the beginning of the al_h.cpi file:

Similar lines must be added at the beginning of other cpi files, in order
to make them readable by ABINIT.

Line 1 is simply a header, that might include any information, and that will
be printed without modification in the output of ABINIT.

Line 2 describes:

the atomic number (zatom);

the ionic charge (zion, number of valence electrons);

the date of pseudopotential generation.

The two first information are crucial, the third one is not
really important. The atomic number is 1 for Hydrogen, 8 for Oxygen, and so on.
The ionic charge should be the same number as the first number mentioned
in the cpi file (called ‘number of valence electrons’).

Line 3 describes:

the format of the pseudopotential (pspcod; must be 6 for this format);

the XC functional used to generate the pseudopotential (pspxc ; the
same numbers as for the input variable ixc should be used,
see ~abinit/doc/users/abinit_help.html)

the maximal angular momentum of the wavefunctions described
in the pseudopotential file (lmax=0 if only s-wavefunctions are present,
lmax=1 for s and p wfs, lmax=2 for s, p and d wfs … ; lmax+1 must be
equal to the ‘number of pseudopotential components’ mentioned in the cpi
file, as the second number of the first line)

the angular momentum of the potential to be used as local pseudopotential
(lloc=0 if s-potential is local; lloc=1 if p-potential is local ; … )

the number of radial mesh points (mmax, same meaning as in the cpi file;
first number on the 12th line)

the last number can be set to 0 .

Line 4 describes 3 parameters needed to read the model core-charge
if core correction is needed.
- rchrg: radius at which the core charge vanish (i.e. cut-off in a.u.)
- fchrg: amplitude of core charge (if =0 non core-correction performed,
if >0 core-correction is applied). The specific value of fchrg
has no physical meaning in fhi98pp scheme of core correction.
- qchrg: integrated model core charge (it’s not actually used by
abinit, and can be set to any value)

rchrg can be inferred by the pp file. Indeed, if the pp has been generated
with the core-correction option, at the end of ‘cpi’ file there will be:

do i=1,mmax
rad(i), f(i), f1(i), f2(i)
end do

that is, the radial grid, the core charge (f), and their first(f1)
and second (f2) derivative on the radial mesh; rchrg can be equal
to any value of rad(i) to which f,f1 and f2 are reasonably vanished.

Line 5-7 have no interest up to now.

A pseudopotential with format 6 will be treated by
the routine psp6in.f, that calls psp5lo.f (local part) and psp5nl.f (non-local part).
There is no psp6lo.f or psp6nl.f.

The integral of (V(r)+Zion/r) r^2 in psp5lo.f is performed
from 0 to the highest allowed radius (usually about 100 a.u.),
except that beyond 20 a.u. no value of abs(V(r)) larger than 2.0d-8 is tolerated.
This will allow to cut off spurious behaviour of pseudopotential whose data file
is written in single precision.